"Cryopumping" or "cryogenic pumping" is the technique of producing low pressures within an enclosed vessel by condensing or adsorbing the gases within the vessel on surfaces cooled to cryogenic temperatures. Cryopumping generally takes place in two or more stages. Gases called Type I gases including water vapor, carbon dioxide and halogens among others with moderately low boiling points are frozen on first stage cryopanels cooled to temperatures of approximately 100.degree. K.
Gases with lower boiling points, called Type II gases including nitrogen and argon among others are frozen onto second stage cryopanels cooled to approximately 20.degree. K.
The lowest boiling point gases, including hydrogen, helium and neon called Type III gases, are cryogenically adsorbed on adsorbents such as molecular sieve or activated charcoal which are attached to surfaces in the form of a box or trap and cooled to temperatures below 20.degree. K. The box or trap is often referred to as the primary pumping surface or primary cryopanel.
Cryopumps have found particular usage by being attached to chambers in which operations are to be performed requiring very low pressures. Examples of such operations include the deposition of metallic and non-metallic films having specific electrical or optical properties. These films are used in the semiconductor industry in the manufacture of integrated circuits and in the optical industry in the manufacture of lenses, filters and mirrors. In many such processes, hydrogen is liberated as a by-product of watermetal reactions or by ionization of water vapor. The capacity of typical cryopumps for Type III (cryosorbed) gases such as hydrogen is generally much less than for the Type I or Type II gases, which are frozen. Consequently, the adsorbent in the pump becomes saturated after a relatively few number of hours of operation. In order to renew the adsorbent capacity, the adsorbent must be warmed and the cryosorbed gases devolved. This regeneration is normally accomplished by inactivating the cryopump and warming it. The gases evolved as the pump warms are removed by secondary pumping means.
However, insofar as the operation being performed is concerned, this is down time. The down time for regeneration, as the process is called, is frequently as long as the time that the cryopump is operative prior to saturation.
This invention is particularly directed to a means for removing hydrogen from a sorbent substantially reducing the down time of the cryopump.